Doping for Semiconductor Device with Conductive Feature

ABSTRACT

The present disclosure relates generally to doping for conductive features in a semiconductor device. In an example, a structure includes an active region of a transistor. The active region includes a source/drain region, and the source/drain region is defined at least in part by a first dopant having a first dopant concentration. The source/drain region further includes a second dopant with a concentration profile having a consistent concentration from a surface of the source/drain region into a depth of the source/drain region. The consistent concentration is greater than the first dopant concentration. The structure further includes a conductive feature contacting the source/drain region at the surface of the source/drain region.

BACKGROUND

With the increasing down-sizing of integrated circuits, the silicideregions, and hence the contact between the contact plugs and thesilicide regions, are also becoming increasingly smaller. Accordingly,contact resistance may become increasingly higher. For example, in FinField-Effect Transistors (FinFETs), the fins are very narrow, causingthe contact areas between the contacts and the fins to be very small.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a three-dimensional view of an example of simplified FinField-Effect Transistors (FinFETs) in accordance with some embodiments.

FIGS. 2A-B, 3A-B, 4A-B, 5A-B, 6A-B, 7A-B, 8A-B, 9A-B, 10A-B, 11A-B,12A-B, 13A-B, 14A-B, 15A-B, 16A-B, and 17A-B are cross-sectional viewsof intermediate stages in an example process of forming one or moreFinFETs in accordance with some embodiments.

FIGS. 18A-B and 19A-B are cross-sectional views of intermediate stagesin another example process of forming one or more FinFETs in accordancewith some embodiments.

FIG. 20 is a cross-sectional view of a conductive feature andsource/drain region in accordance with some embodiments.

FIG. 21 is a graph illustrating various dopant profiles in accordancewith some embodiments.

FIG. 22 is a cross-sectional view of a portion of an example devicestructure in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Conductive features, e.g., including contacts, to source/drain regionsof transistors, for example, and methods for forming such conductivefeatures are described. In some examples, a dopant, such as gallium insome examples, is implanted into source/drain regions with a profilethat has a platform concentration near a surface of the source/drainregion that is greater than a doping concentration of a remainder of thesource/drain region. The platform concentration can reduce a resistanceof a contact to the source/drain region.

Example conductive features described and illustrated herein areimplemented in Fin Field-Effect Transistors (FinFETs); however,conductive features within the scope of this disclosure may also beimplemented in planar transistors and/or other semiconductor devices.Further, intermediate stages of forming FinFETs are illustrated. Someembodiments described herein are described in the context of FinFETsformed using a replacement gate process. In other examples, a gate-firstprocess may be used. Some variations of the example methods andstructures are described. A person having ordinary skill in the art willreadily understand other modifications that may be made that arecontemplated within the scope of other embodiments. Although methodembodiments may be described in a particular order, various other methodembodiments may be performed in any logical order and may include feweror more steps described herein.

FIG. 1 illustrates an example of simplified FinFETs 40 in athree-dimensional view. Other aspects not illustrated in or describedwith respect to FIG. 1 may become apparent from the following figuresand description. The structure in FIG. 1 may be electrically connectedor coupled in a manner to operate as, for example, one transistor ormore, such as four transistors.

The FinFETs 40 comprise fins 46 a and 46 b on a substrate 42. Thesubstrate 42 includes isolation regions 44, and the fins 46 a and 46 beach protrude above and from between neighboring isolation regions 44.Gate dielectrics 48 a and 48 b are along sidewalls and over top surfacesof the fins 46 a and 46 b, and gate electrodes 50 a and 50 b are overthe gate dielectrics 48 a and 48 b, respectively. Source/drain regions52 a-f are disposed in respective regions of the fins 46 a and 46 b.Source/drain regions 52 a and 52 b are disposed in opposing regions ofthe fin 46 a with respect to the gate dielectric 48 a and gate electrode50 a. Source/drain regions 52 b and 52 c are disposed in opposingregions of the fin 46 a with respect to the gate dielectric 48 b andgate electrode 50 b. Source/drain regions 52 d and 52 e are disposed inopposing regions of the fin 46 b with respect to the gate dielectric 48a and gate electrode 50 a. Source/drain regions 52 e and 52 f aredisposed in opposing regions of the fin 46 b with respect to the gatedielectric 48 b and gate electrode 50 b.

In some examples, four transistors may be implemented by: (1)source/drain regions 52 a and 52 b, gate dielectric 48 a, and gateelectrode 50 a; (2) source/drain regions 52 b and 52 c, gate dielectric48 b, and gate electrode 50 b; (3) source/drain regions 52 d and 52 e,gate dielectric 48 a, and gate electrode 50 a; and (4) source/drainregions 52 e and 52 f, gate dielectric 48 b, and gate electrode 50 b. Asindicated, some source/drain regions may be shared between varioustransistors, and other source/drain regions that are not illustrated asbeing shared may be shared with neighboring transistors that are notillustrated, for example. In some examples, various ones of thesource/drain regions may be connected or coupled together such thatFinFETs are implemented as two functional transistors. For example, ifneighboring (e.g., as opposed to opposing) source/drain regions 52 a-fare electrically connected, such as through coalescing the regions byepitaxial growth (e.g., source/drain regions 52 a and 52 d beingcoalesced, source/drain regions 52 b and 52 e being coalesced, etc.),two functional transistors may be implemented. Other configurations inother examples may implement other numbers of functional transistors.

FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section A-A is in a plane along, e.g., channels inthe fin 46 a between opposing source/drain regions 52 a-f. Cross-sectionB-B is in a plane perpendicular to cross-section A-A and is acrosssource/drain region 52 a in fin 46 a and across source/drain region 52 din fin 46 b. Subsequent figures refer to these reference cross-sectionsfor clarity.

FIGS. 2A-B through 17A-B are cross-sectional views of intermediatestages in an example process of forming one or more FinFETs inaccordance with some embodiments. In FIGS. 2A-B through 17A-B, figuresending with an “A” designation illustrate cross-sectional views along across-section similar to cross-section A-A in FIG. 1, and figures endingwith a “B” designation illustrate cross-sectional views along across-section similar to cross-section B-B in FIG. 1. In some figures,some reference numbers of components or features illustrated therein maybe omitted to avoid obscuring other components or features; this is forease of depicting the figures.

FIGS. 2A and 2B illustrate a semiconductor substrate 70. Thesemiconductor substrate 70 may be or include a bulk semiconductorsubstrate, a semiconductor-on-insulator (SOI) substrate, or the like,which may be doped (e.g., with a p-type or an n-type dopant) or undoped.Generally, an SOI substrate comprises a layer of a semiconductormaterial formed on an insulator layer. The insulator layer may be, forexample, a buried oxide (BOX) layer, a silicon oxide layer, or the like.The insulator layer is provided on a substrate, typically a silicon orglass substrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the semiconductor substrate layer may include silicon (Si);germanium (Ge); a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, or GaInAsP; or a combination thereof.

FIGS. 3A and 3B illustrate the formation of fins 74 in the semiconductorsubstrate 70. In the illustrated example, a mask 72 (e.g., a hard mask)is used in forming the fins 74. For example, one or more mask layers aredeposited over the semiconductor substrate 70, and the one or more masklayers are then patterned into the mask 72. In some examples, the one ormore mask layers may include or be silicon nitride, silicon oxynitride,silicon carbide, silicon carbon nitride, the like, or a combinationthereof, and may be deposited by chemical vapor deposition (CVD),physical vapor deposition (PVD), atomic layer deposition (ALD), oranother deposition technique. The one or more mask layers may bepatterned using photolithography. For example, a photo resist can beformed on the one or more mask layers, such as by using spin-on coating,and patterned by exposing the photo resist to light using an appropriatephotomask. Exposed or unexposed portions of the photo resist may then beremoved depending on whether a positive or negative resist is used. Thepattern of the photo resist may then be transferred to the one or moremask layers, such as by using a suitable etch process, which forms themask 72. The etch process may include a reactive ion etch (RIE), neutralbeam etch (NBE), the like, or a combination thereof. The etching may beanisotropic. Subsequently, the photo resist is removed in an ashing orwet strip processes, for example.

Using the mask 72, the semiconductor substrate 70 may be etched suchthat trenches 76 are formed between neighboring pairs of fins 74 andsuch that the fins 74 protrude from the semiconductor substrate 70. Theetch process may include a RIE, NBE, the like, or a combination thereof.The etching may be anisotropic.

FIGS. 4A and 4B illustrate the formation of isolation regions 78, eachin a corresponding trench 76. The isolation regions 78 may include or bean insulating material such as an oxide (such as silicon oxide), anitride, the like, or a combination thereof, and the insulating materialmay be formed by a high density plasma CVD (HDP-CVD), a flowable CVD(FCVD) (e.g., a CVD-based material deposition in a remote plasma systemand post curing to make it convert to another material, such as anoxide), the like, or a combination thereof. Other insulating materialsformed by any acceptable process may be used. In the illustratedembodiment, the isolation regions 78 include silicon oxide that isformed by a FCVD process. A planarization process, such as a chemicalmechanical polish (CMP), may remove any excess insulating material andany remaining mask 72 to form top surfaces of the insulating materialand top surfaces of the fins 74 to be coplanar. The insulating materialmay then be recessed to form the isolation regions 78. The insulatingmaterial is recessed such that the fins 74 protrude from betweenneighboring isolation regions 78, which may, at least in part, therebydelineate the fins 74 as active areas on the semiconductor substrate 70.The insulating material may be recessed using an acceptable etchingprocess, such as one that is selective to the material of the insulatingmaterial. For example, a chemical oxide removal using a CERTAS® etch oran Applied Materials SICONI tool or dilute hydrofluoric (dHF) acid maybe used. Further, top surfaces of the isolation regions 78 may have aflat surface as illustrated, a convex surface, a concave surface (suchas dishing), or a combination thereof, which may result from an etchprocess.

A person having ordinary skill in the art will readily understand thatthe process described with respect to FIGS. 2A-B through 4A-B is justone example of how fins 74 may be formed. In other embodiments, adielectric layer can be formed over a top surface of the semiconductorsubstrate 70; trenches can be etched through the dielectric layer;homoepitaxial structures can be epitaxially grown in the trenches; andthe dielectric layer can be recessed such that the homoepitaxialstructures protrude from the dielectric layer to form fins. In stillother embodiments, heteroepitaxial structures can be used for the fins.For example, the fins 74 can be recessed (e.g., after planarizing theinsulating material of the isolation regions 78 and before recessing theinsulating layer), and a material different from the fins may beepitaxially grown in their place. In an even further embodiment, adielectric layer can be formed over a top surface of the semiconductorsubstrate 70; trenches can be etched through the dielectric layer;heteroepitaxial structures can be epitaxially grown in the trenchesusing a material different from the semiconductor substrate 70; and thedielectric layer can be recessed such that the heteroepitaxialstructures protrude from the dielectric layer to form fins. In someembodiments where homoepitaxial or heteroepitaxial structures areepitaxially grown, the grown materials may be in situ doped duringgrowth, which may obviate prior implanting of the fins although in situand implantation doping may be used together. Still further, it may beadvantageous to epitaxially grow a material for an n-type devicedifferent from the material in for a p-type device. In variousembodiments, the fins 74 may comprise silicon, silicon germanium(Si_(x)Ge_(1-x), where x can be between approximately 0 and 100),silicon carbide, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,materials for forming a III-V compound semiconductor include InAs, AlAs,GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and the like.

FIGS. 5A and 5B illustrate the formation of dummy gate stacks on thefins 74. Each dummy gate stack comprises an etch stop 80, a dummy gate82, and a mask 84. The etch stop 80, dummy gate 82, and mask 84 may beformed by sequentially depositing respective layers and patterning thoselayers. For example, a layer for the etch stop 80 may include or besilicon oxide, silicon nitride, the like, or multilayers thereof, andmay be thermally grown or deposited, such as by plasma-enhanced CVD(PECVD), ALD, or another deposition technique. A layer for the dummygate 82 may include or be silicon (e.g., polysilicon) or anothermaterial deposited by CVD, PVD, or another deposition technique. A layerfor the mask 84 may include or be silicon nitride, silicon oxynitride,silicon carbon nitride, the like, or a combination thereof, deposited byCVD, PVD, ALD, or another deposition technique. The layers for the mask84, dummy gate 82, and etch stop 80 may then be patterned, for example,using photolithography and one or more etch processes, like describedabove with respect to FIGS. 3A and 3B, to form the mask 84, dummy gate82, and etch stop 80 for each gate stack.

In the illustrated example, a dummy gate stack is implemented for areplacement gate process. In other examples, a gate-first process may beimplemented using gate stacks including, for example, a gate dielectricin the place of the etch stop 80, and a gate electrode in the place ofthe dummy gate 82. In some gate-first processes, the gate stack may beformed using similar processes and materials as described with respectto the dummy gate stacks; although in other examples, other processes ormaterials may be implemented. For example, a gate dielectric may includeor be a high-k dielectric material, such as having a k value greaterthan about 7.0, which may include a metal oxide or silicate of Hf, Al,Zr, La, Mg, Ba, Ti, Pb, multilayers thereof, or a combination thereof. Agate dielectric may also be deposited by molecular-beam deposition(MBD), ALD, PECVD, or another deposition technique. A gate electrode mayalso include or be a metal-containing material such as TiN, TaN, TaC,Co, Ru, Al, multi-layers thereof, or a combination thereof.

FIGS. 6A and 6B illustrate the formation of gate spacers 86. Gatespacers 86 are formed along sidewalls of the dummy gate stacks (e.g.,sidewalls of the etch stop 80, dummy gate 82, and mask 84). The gatespacers 86 may be formed by conformally depositing one or more layersfor the gate spacers 86 and anisotropically etching the one or morelayers, for example. The one or more layers for the gate spacers 86 mayinclude or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, multi-layers thereof, or a combination thereof, andthe etch process can include a RIE, NBE, or another etching process.

FIGS. 7A and 7B illustrate the formation of recesses 90 for source/drainregions. As illustrated, the recesses 90 are formed in the fins 74 onopposing sides of the dummy gate stacks. The recessing can be by an etchprocess. The etch process can be isotropic or anisotropic, or further,may be selective with respect to one or more crystalline planes of thesemiconductor substrate 70. Hence, the recesses 90 can have variouscross-sectional profiles based on the etch process implemented. The etchprocess may be a dry etch, such as a RIE, NBE, or the like, or a wetetch, such as using tetramethyalammonium hydroxide (TMAH), ammoniumhydroxide (NH₄OH), or another etchant.

FIGS. 8A and 8B illustrate the formation of epitaxy source/drain regions92 in the recesses 90. The epitaxy source/drain regions 92 may includeor be silicon germanium (Si_(x)Ge_(1-x), where x can be betweenapproximately 0 and 100), silicon carbide, silicon phosphorus, pure orsubstantially pure germanium, a III-V compound semiconductor, a II-VIcompound semiconductor, or the like. For example, materials for forminga III-V compound semiconductor include InAs, AlAs, GaAs, InP, GaN,InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and the like. The epitaxysource/drain regions 92 may be formed in the recesses 90 by epitaxiallygrowing a material in the recesses 90, such as by metal-organic CVD(MOCVD), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), vaporphase epitaxy (VPE), selective epitaxial growth (SEG), the like, or acombination thereof. As illustrated in FIGS. 8A and 8B, due to blockingby the isolation regions 78, epitaxy source/drain regions 92 are firstgrown vertically in recesses 90, during which time the epitaxysource/drain regions 92 do not grow horizontally. After the recesses 90are fully filled, the epitaxy source/drain regions 92 may grow bothvertically and horizontally to form facets, which may correspond tocrystalline planes of the semiconductor substrate 70. In some examples,different materials are used for epitaxy source/drain regions for p-typedevices and n-type devices. Appropriate masking during the recessing orepitaxial growth may permit different materials to be used in differentdevices.

A person having ordinary skill in the art will also readily understandthat the recessing and epitaxial growth of FIGS. 7A-B and 8A-B may beomitted, and that source/drain regions may be formed by implantingdopants into the fins 74. In some examples where epitaxy source/drainregions 92 are implemented, the epitaxy source/drain regions 92 may alsobe doped, such as by in-situ doping during epitaxial growth and/or byimplanting dopants into the epitaxy source/drain regions 92 afterepitaxial growth. Example dopants can include or be, for example, boronfor a p-type device and phosphorus or arsenic for an n-type device,although other dopants may be used. The epitaxy source/drain regions 92(or other source/drain region) may have a dopant concentration in arange from about 10¹⁹ cm⁻³ to about 10²¹ cm⁻³. Hence, a source/drainregion may be delineated by doping (e.g., by implantation and/or in situduring epitaxial growth, if appropriate) and/or by epitaxial growth, ifappropriate, which may further delineate the active area in which thesource/drain region is delineated.

FIGS. 9A and 9B illustrate an amorphization implant 94. Theamorphization implant 94 may be omitted in some implementations. In someexamples, the amorphization implant 94 includes implanting an impurityspecies into the epitaxy source/drain regions 92 to make upper portions96 of the epitaxy source/drain regions 92 amorphous. The upper portions96 that are made amorphous can extend from respective upper surfaces ofthe epitaxy source/drain regions 92 to a depth from about 2 nm to about20 nm, for example. In some examples, such as for a p-type device, theepitaxy source/drain regions 92 are Si_(x)Ge_(1-x), and germanium is thespecies implanted to amorphize the upper portions 96 of the epitaxysource/drain regions 92. In such examples, the implant energy can be ina range from about 1 keV to about 15 keV, such as about 10 keV, with adosage concentration in a range from about 5×10¹³ cm⁻² to about 5×10¹⁴cm⁻².

FIGS. 10A and 10B illustrate a dopant implant 98 into the upper portions96 of the epitaxy source/drain regions 92. The dopant implant 98 mayimplant dopants to the upper portions 96 to reduce a contact resistancebetween the respective epitaxy source/drain region 92 and a conductivefeature (e.g., including a contact) that is subsequently formed. In someexamples, the species of the dopant used for the dopant implant 98 mayamorphize the upper portions 96 when implanted (and hence, may bereferred to as self-amorphizing). In those examples or in differentexamples, the amorphization implant 94 of FIGS. 9A and 9B may beomitted. The dopant implant 98 may implant dopants to the upper portions96 such that the upper portions 96 have a consistent concentration ofthe dopant from the respective upper surfaces of the upper portions 96to depths of equal to or greater than 5 nm, equal to or greater than 10nm, or equal to or greater than 15 nm. The consistent concentration ofthe dopant can be greater than the concentration of the dopant thatdelineates, at least in part, the source/drain regions (e.g., formed byimplantation and/or in situ doping during epitaxial growth). Theconcentration of the dopant in the epitaxy source/drain regions 92 maydecrease from the consistent concentration into further depths of theepitaxy source/drain regions 92. Additional example details of thedopant implant 98 and the concentrations of the dopant resulting fromthe dopant implant 98 are described with respect to FIGS. 20 and 21below.

In some examples, such as for a p-type device, the epitaxy source/drainregions 92 are Si_(x)Ge_(1-x), and gallium is the species implanted intothe upper portions 96 of the epitaxy source/drain regions 92 for thedopant implant 98. In such examples, the implant energy can be in arange from about 0.5 keV to about 10 keV, with a dosage concentration ina range from about 1×10¹⁵ cm⁻² to about 1×10¹⁶ cm⁻². The consistentconcentration of gallium from the upper surfaces of the epitaxysource/drain regions 92 to the depth may be in a range from about 10²¹cm⁻³ to about 10²² cm⁻³, and more particularly, about 5×10²¹ cm⁻³.

After the dopant implant 98, an anneal is performed to activate thedopants and recrystallize the upper portions 96 that were amorphized(e.g., by the amorphization implant 94 and/or by the dopant implant 98).The anneal, in some examples, may be at a temperature in a range fromabout 600° C. to about 900° C. for a duration in a range equal to orless than about one minute, equal to or less than about 12 seconds, orequal to or less than about 1 second. In other examples, the anneal maybe a laser anneal performed for a duration of several nanoseconds, suchas equal to or less than about 100 ns. In further examples, the annealmay be a melting anneal performed for a duration of a few nanoseconds,such as about 1 ns.

FIGS. 11A and 11B illustrate the formation of one or more dielectriclayers 100. The one or more dielectric layers 100 may include an etchstop layer (ESL) and an interlayer dielectric (ILD), for example.Generally, an etch stop layer can provide a mechanism to stop an etchingprocess when forming, e.g., contacts or vias. An etch stop layer may beformed of a dielectric material having a different etch selectivity fromadjacent layers, for example, the interlayer dielectric. The etch stoplayer may be conformally deposited over the epitaxy source/drain regions92, dummy gate stacks, spacers 86, and isolation regions 78. The etchstop layer may comprise or be silicon nitride, silicon carbon nitride,silicon carbon oxide, carbon nitride, the like, or a combinationthereof, and may be deposited by CVD, PECVD, ALD, or another depositiontechnique. The interlayer dielectric may comprise or be silicon dioxide,a low-K dielectric material (e.g., a material having a dielectricconstant lower than silicon dioxide), such as silicon oxynitride,phosphosilicate glass (PSG), borosilicate glass (BSG),borophosphosilicate glass (BPSG), undoped silicate glass (USG),fluorinated silicate glass (FSG), organosilicate glasses (OSG),SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbon material,a compound thereof, a composite thereof, the like, or a combinationthereof. The interlayer dielectric may be deposited by spin-on, CVD,FCVD, PECVD, PVD, or another deposition technique.

The one or more dielectric layers 100 are formed with top surface(s)coplanar with top surfaces of the dummy gates 82. A planarizationprocess, such as a CMP, may be performed to level the top surface of theone or more dielectric layers 100 with the top surfaces of the dummygates 82. The CMP may also remove the mask 84 (and, in some instances,upper portions of the spacers 86) on the dummy gates 82. Accordingly,top surfaces of the dummy gates 82 are exposed through the one or moredielectric layers 100.

FIGS. 12A and 12B illustrate the replacement of the dummy gate stackswith gate dielectrics 102, gate electrodes 104, and masks 106. The dummygates 82 and etch stops 80 are removed, such as by one or more etchprocesses. The dummy gates 82 may be removed by an etch process, whereinthe etch stops 80 act as etch stop layers, and subsequently, the etchstops 80 can be removed by a different etch process. The etch processescan be, for example, a RIE, NBE, a wet etch, or another etch process.

A layer for the gate dielectrics 102 is formed, e.g., where the dummygates 82 and etch stops 80 were removed. For example, the layer for thegate dielectrics 102 can be conformally deposited along sidewalls of thegate spacers 86, top surfaces and sidewalls of the fins 74 where dummygate stacks were removed, and over the top surface of the one or moredielectric layers 100. The layer for the gate dielectrics 102 can be orinclude silicon oxide, silicon nitride, a high-k dielectric material,multilayers thereof, or other dielectric material. A high-k dielectricmaterial may have a k value greater than about 7.0, and may include ametal oxide of or a metal silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, ora combination thereof. The layer for the gate dielectrics 102 can bedeposited by ALD, PECVD, MBD, or another deposition technique.

A layer for the gate electrodes 104 is formed over the layer for thegate dielectrics 102. The layer for the gate electrodes 104 can fillremaining regions where the dummy gate stacks were removed. The layerfor the gate electrodes may be or comprise a metal-containing materialsuch as TiN, TaN, TaC, Co, Ru, Al, multi-layers thereof, or acombination thereof. The layer for the gate electrodes 104 can bedeposited by ALD, PECVD, MBD, PVD, or another deposition technique.

Portions of the layers for the gate electrodes 104 and the gatedielectrics 102 above the top surface of the one or more dielectriclayers 100 are removed. For example, a planarization process, like aCMP, may remove the portions of the layers for the gate electrodes 104and the gate dielectrics 102 above the top surface of the one or moredielectric layers 100. Subsequently, an etch-back may recess topsurfaces of the gate electrodes 104 and gate dielectrics 102 to a levelbelow the top surface of the one or more dielectric layers 100. Theetch-back may be a RIE, wet etch, or another etch process, for example.The gate electrodes 104 and gate dielectrics 102 may therefore be formedas illustrated in FIG. 12A.

A layer for the masks 106 is formed over the gate electrodes 104 andgate dielectrics 102 (e.g., where the gate electrodes 104 and gatedielectrics 102 have been etched back) and over the one or moredielectric layers 100. The layer for the masks 106 may include or besilicon nitride, silicon oxynitride, silicon carbide, silicon carbonnitride, the like, or a combination thereof, and may be deposited byCVD, PVD, ALD, or another deposition technique. Portions of the layerfor the masks 106 above the top surface of the one or more dielectriclayers 100 are removed. For example, a planarization process, like aCMP, may remove the portions of the layer for masks 106 above the topsurface of the one or more dielectric layers 100, and top surfaces ofthe masks 106 may be formed coplanar with the top surface of the one ormore dielectric layers 100.

As indicated previously, gate stacks with a gate dielectric and gateelectrode may be implemented in a gate-first process rather than areplacement gate process as illustrated. In such examples, some processsteps described with respect to FIGS. 11A-B and 12A-B may be omitted.For example, if a planarization process is used in FIGS. 11A-B, the topsurface of the one or more dielectric layers 100 may remain above topsurfaces of the gate stacks. The removal of dummy gate stacks and thereplacement gate dielectrics, gate electrodes, and masks in FIGS. 12A-Bmay be omitted.

FIGS. 13A and 13B illustrate the formation of openings 110 through theone or more dielectric layers 100 to the epitaxy source/drain regions 92to expose at least respective portions of the epitaxy source/drainregions 92. A mask 112 is formed on the one or more dielectric layers100 and masks 106 for forming the openings 110. A layer for the mask 112may include or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, or a combination thereof, deposited by CVD, PVD, ALD,or another deposition technique. The layer for the mask 112 may then bepatterned, for example, using photolithography and one or more etchprocesses. Using the mask 112, the openings 110 can be formed throughthe one or more dielectric layers 100 using one or more etch processes,such as RIE, NBE, or another etch process.

Although not specifically illustrated, an amorphization implant may beperformed to amorphize upper portions of the epitaxy source/drainregions 92 where silicide regions are to be formed, as described below.The amorphized upper portions of the epitaxy source/drain regions 92 maypermit more efficient and/or faster formation of silicide compared toformation of silicide without using an amorphization implant. In someexamples, the species used for the amorphization implant is germanium oranother species.

FIGS. 14A and 14B illustrate the formation of a metal layer 114 and abarrier layer 116 in the openings 110. The metal layer 114 isconformally deposited in the openings 110, and the barrier layer 116 isconformally deposited on the metal layer 114. Particularly, the metallayer 114 is deposited on upper surfaces of the epitaxy source/drainregions 92 exposed by the openings 110, and along other surfaces of theopenings 110. The metal layer 114 may be or comprise, for example,titanium, cobalt, nickel, the like or a combination thereof, and may bedeposited by ALD, CVD, or another deposition technique. The metal layer114 may be deposited to a thickness in a range from 2 nm to about 15 nm,for example. The barrier layer 116 may be or comprise titanium nitride,titanium oxide, tantalum nitride, tantalum oxide, the like, or acombination thereof, and may be deposited by ALD, CVD, or anotherdeposition technique. The barrier layer 116 may be deposited to athickness in a range from 2 nm to about 15 nm, for example.

FIGS. 15A and 15B illustrate the formation of silicide regions 118 onupper portions of the epitaxy source/drain regions 92. The silicideregions 118 may be formed by reacting upper portions of the epitaxysource/drain regions 92 with the metal layer 114 and/or barrier layer116. An anneal is performed to facilitate the reaction of the epitaxysource/drain regions 92 with the metal layer 114 and/or barrier layer116. The anneal may be at a temperature in a range from about 500° C. toabout 600° C. for a duration of greater than or equal to about 10seconds. The silicide regions 118 may have a thickness in a range from 2nm to about 20 nm, for example. In some examples, an etch may beperformed to remove unreacted portions of the metal layer 114 and/orbarrier layer 116.

FIGS. 16A and 16B illustrate the formation of contacts 120 filling theopenings 110. The contacts 120 may be or comprise tungsten, copper,aluminum, gold, silver, alloys thereof, the like, or a combinationthereof, and may be deposited by CVD, ALD, PVD, or another depositiontechnique. After the material of the contacts 120 is deposited, excessmaterial may be removed by using a planarization process, such as a CMP,for example. The planarization process may remove excess material of thecontacts 120, barrier layer 116, metal layer 114, and mask 112 fromabove the top surface of the one or more dielectric layers 100. Hence,top surfaces of the contacts 120, barrier layer 116, metal layer 114,and one or more dielectric layers 100 may be coplanar. Accordingly,conductive features including the contacts 120, barrier layer 116, metallayer 114, and/or silicide regions 118 may be formed to the epitaxysource/drain regions 92.

Although the conductive features (e.g., including the contacts 120) aredepicting as having a certain configuration in the figures, theconductive features can have any configuration. For example, separateconductive features may be formed to separate epitaxy source/drainregions 92. A person having ordinary skill in the art will readilyunderstand modifications to process steps described herein to achievedifferent configurations.

FIGS. 17A and 17B illustrate the formation of one or more dielectriclayers 122 and conductive features 124 in the one or more dielectriclayers 122. The one or more dielectric layers 122 may include an etchstop layer (ESL) and an interlayer dielectric (ILD) or intermetaldielectric (IMD), for example. The etch stop layer may be deposited overthe one or more dielectric layers 100, contacts 120, masks 106, etc. Theetch stop layer may comprise or be silicon nitride, silicon carbonnitride, silicon carbon oxide, carbon nitride, the like, or acombination thereof, and may be deposited by CVD, PECVD, ALD, or anotherdeposition technique. The interlayer dielectric or intermetal dielectricmay comprise or be silicon dioxide, a low-K dielectric material, such assilicon oxynitride, PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y),Spin-On-Glass, Spin-On-Polymers, silicon carbon material, a compoundthereof, a composite thereof, the like, or a combination thereof. Theinterlayer dielectric or intermetal dielectric may be deposited byspin-on, CVD, FCVD, PECVD, PVD, or another deposition technique.

Recesses and/or openings are formed in and/or through the one or moredielectric layers 122 where the conductive features 124 are to beformed. The one or more dielectric layers 122 may be patterned with therecesses and/or openings, for example, using photolithography and one ormore etch processes. The conductive features 124 may then be formed inthe recesses and/or openings. The conductive features 124 may include abarrier layer and conductive material formed on the barrier layer, forexample. The barrier layer can be conformally deposited in the recessesand/or openings and over the one or more dielectric layers 122. Thebarrier layer may be or comprise titanium nitride, titanium oxide,tantalum nitride, tantalum oxide, the like, or a combination thereof,and may be deposited by ALD, CVD, or another deposition technique. Theconductive material may be or comprise tungsten, copper, aluminum, gold,silver, alloys thereof, the like, or a combination thereof, and may bedeposited by CVD, ALD, PVD, or another deposition technique. After thematerial of the conductive features 124 is deposited, excess materialmay be removed by using a planarization process, such as a CMP, forexample. The planarization process may remove excess material of theconductive features 124 from above a top surface of the one or moredielectric layers 122. Hence, top surfaces of the conductive features124 and the one or more dielectric layers 122 may be coplanar. Theconductive features 124 may be or may be referred to as contacts, vias,conductive lines, etc.

FIGS. 18A-B through 19A-B are cross-sectional views of intermediatestages in an example process of forming one or more FinFETs inaccordance with some embodiments. In FIGS. 18A-B through 19A-B, figuresending with an “A” designation illustrate cross-sectional views along across-section similar to cross-section A-A in FIG. 1, and figures endingwith a “B” designation illustrate cross-sectional views along across-section similar to cross-section B-B in FIG. 1. In some figures,some reference numbers of components or features illustrated therein maybe omitted to avoid obscuring other components or features; this is forease of depicting the figures.

In the example process of FIGS. 18A-B through 19A-B, processing proceedsas described above with respect to FIGS. 2A-B through 8A-B and 11A-Bthrough the formation of openings 110 through the one or more dielectriclayers 100 in FIGS. 13A-B. In this example, the processing shown inFIGS. 9A-B and 10A-B is omitted. The processing in this example resumesat FIGS. 18A-B.

FIGS. 18A and 18B illustrate an amorphization implant 140. Theamorphization implant 140 may be omitted in some implementations. Insome examples, the amorphization implant 140 includes implanting animpurity species through the openings 110 through the one or moredielectric layers 100 into the epitaxy source/drain regions 92 to makeupper portions 142 of the epitaxy source/drain regions 92 amorphous. Theupper portions 142 that are made amorphous can extend from respectiveupper surfaces of the epitaxy source/drain regions 92 to a depth fromabout 2 nm to about 20 nm, for example. In some examples, such as for ap-type device, the epitaxy source/drain regions 92 are Si_(x)Ge_(1-x),and germanium is the species implanted to amorphize the upper portions142 of the epitaxy source/drain regions 92. In such examples, theimplant energy can be in a range from about 1 keV to about 15 keV, suchas about 10 keV, with a dosage concentration in a range from about5×10¹³ cm⁻² to about 5×10¹⁴ cm⁻².

FIGS. 19A and 19B illustrate a dopant implant 144 into the upperportions 142 of the epitaxy source/drain regions 92. The dopant implant144 may implant dopants through the openings 110 through the one or moredielectric layers 100 to the upper portions 142 to reduce a contactresistance between the respective epitaxy source/drain region 92 and aconductive feature (e.g., including a contact) that is subsequentlyformed. In some examples, the species of the dopant used for the dopantimplant 144 may amorphize the upper portions 142 when implanted (andhence, may be referred to as self-amorphizing). In those examples or indifferent examples, the amorphization implant 140 of FIGS. 18A and 18Bmay be omitted. The dopant implant 144 may implant dopants to the upperportions 142 such that the upper portions 142 have a consistentconcentration of the dopant from the respective upper surfaces of theupper portions 142 to depths of equal to or greater than 5 nm, equal toor greater than 10 nm, or equal to or greater than 15 nm. The consistentconcentration of the dopant can be greater than the concentration of thedopant that delineates, at least in part, the source/drain regions(e.g., formed by implantation and/or in situ doping during epitaxialgrowth). The concentration of the dopant in the epitaxy source/drainregions 92 may decrease from the consistent concentration into furtherdepths of the epitaxy source/drain regions 92. Additional exampledetails of the dopant implant 144 and the concentrations of the dopantresulting from the dopant implant 144 are described with respect toFIGS. 20 and 21 below.

In some examples, such as for a p-type device, the epitaxy source/drainregions 92 are Si_(x)Ge_(1-x), and gallium is the species implanted intothe upper portions 142 of the epitaxy source/drain regions 92 for thedopant implant 144. In such examples, the implant energy can be in arange from about 0.5 keV to about 10 keV, with a dosage concentration ina range from about 1×10¹⁵ cm⁻² to about 1×10¹⁶ cm⁻². The consistentconcentration of gallium from the upper surfaces of the epitaxysource/drain regions 92 to the depth may be in a range from about 10²¹cm⁻³ to about 10²² cm⁻³, and more particularly, about 5×10²¹ cm⁻³.

After the dopant implant 144, an anneal is performed to activate thedopants and recrystallize the upper portions 142 that were amorphized(e.g., by the amorphization implant 140 and/or by the dopant implant144). The anneal, in some examples, may be at a temperature in a rangefrom about 600° C. to about 900° C. for a duration in a range equal toor less than about one minute, equal to or less than about 12 seconds,or equal to or less than about 1 second. In other examples, the annealmay be a laser anneal performed for a duration of several nanoseconds,such as equal to or less than about 100 ns. In further examples, theanneal may be a melting anneal performed for a duration of a fewnanoseconds, such as about 1 ns.

In the example process of FIGS. 18A-B through 19A-B, processing resumeswith an amorphization implant, if implemented, through the processing ofFIGS. 14A-B through FIGS. 17A-B.

FIG. 20 illustrates a cross-sectional view of the conductive feature(e.g., including the contact 120) and epitaxy source/drain region 92 inaccordance with some embodiments. The epitaxy source/drain region 92includes a platform dopant region 200 and a tailing dopant region 202.The dopant concentration, e.g., of the dopant implanted in FIGS. 10A-Band 19A-B, in the platform dopant region 200 is substantially consistentor constant throughout the platform dopant region 200. From thesubstantially consistent or constant dopant concentration in theplatform dopant region 200, the dopant concentration decreases with agradient in the tailing dopant region 202.

FIG. 21 is a graph illustrating various dopant profiles in accordancewith some embodiments. The graph illustrates an as-implanted dopantprofile 300 (e.g., with or without an amorphization implant precedingthe dopant implant), a first as-annealed dopant profile 302 without apreceding amorphization implant, and a second as-annealed dopant profile304 with a preceding amorphization implant. The illustrated dopantprofiles are for gallium implanted into silicon germanium. Anyamorphization implants for the profiles 300 and 304 use germanium as theimplant species, and anneals for the profiles 302 and 304 are a rapidthermal anneal at 1000° C. Other dopants, materials into which thedopant is implanted, amorphization species, or anneals may be used inother examples.

As illustrated, each of the profiles 300, 302, and 304 have asubstantially consistent or constant dopant concentration throughout adepth up to about 8 nm (e.g., for the profile 302) or about 12 nm (e.g.,for the profiles 300 and 304). These substantially consistent orconstant dopant concentrations may be the platform dopant region 200 insome examples. From these substantially consistent or constant dopantconcentrations (e.g., beginning at a depth of about 8 nm, e.g., for theprofile 302, or about 12 nm, e.g., for the profiles 300 and 304), thedopant concentrations decrease as the profile extends away from thesubstantially consistent or constant dopant concentrations (e.g., asdepth increases) in the profiles 300, 302, and 304.

As described previously, in some examples, the dopant species for thedopant implant may be gallium. Gallium may, in some examples, haveadvantageous aspects. For example, gallium has a higher solid solubilityin germanium than other dopant species, such as boron. Hence, when agermanium content in the epitaxy source/drain regions 92 is high,gallium may have a higher activation, and hence, contribute more holes,in comparison to other dopants. Additionally, gallium (e.g., Ga⁶⁹) maybe larger, on an atomic scale, than other species, such as boron. Thismay permit implants of gallium to be self-amorphizing, and hence, anamorphization implant preceding an implant of gallium may be omitted.

Furthermore, the platform concentrations of the doping profilesillustrated in FIG. 21 that can be achieved by implanting gallium canfacilitate having an appropriate concentration at a surface of theepitaxy source/drain regions 92 and/or silicide regions 118. Forexample, in some example processes, some loss of the epitaxysource/drain regions 92 may be realized as a result of etching, such asduring processing illustrated in FIGS. 13A-B. In some examples, evenwith some loss of the epitaxy source/drain regions 92, such as a 5 nmloss (e.g., such that the platform concentration remains through a depthof 3 nm, 5 nm, 7 nm, or 10 nm in the epitaxy source/drain regions 92),the platform concentration may permit the concentration of the dopant atthe surface to remain substantially unchanged. Other dopant species maynot be able to achieve a platform concentration, and hence, with someloss of the epitaxy source/drain regions 92, a concentration of thedopant at the surface can decrease. Accordingly, in some examples, ahigh concentration of dopant may be achieved that can reduce a contactresistance to the epitaxy source/drain region 92 (e.g., between theconductive feature 120 and the epitaxy source/drain region 92).

Also, gallium may be less likely to diffuse than other dopant species.This may permit the dopant profile to remain close to the as-implanteddopant profile after subsequent processing, such as after an anneal.This may permit more flexibility in processing for thermal budgets. Forexample, the dopant implant may be performed before various hightemperature processes. Further, since gallium may be less prone todiffusing, short channel effects in a transistor, like a FinFET, may bemitigated.

As previously indicated, the device structures may vary in differentimplementations. FIG. 22 illustrates a cross-sectional view of a portionof another implementation of a device structure in accordance with someembodiments. The structure of FIG. 22 may be referred to as a “crown”structure, whereas the structure of, e.g., FIG. 4B may be referred to asa “non-crown” structure. As depicted in FIG. 22, the lower surfaces ofthe isolation regions 78 may be at varying levels. This may be obtainedduring patterning the semiconductor substrate 70 in forming the fins 74,such as by two or more patterning and etching processes.

An embodiment is a structure. The structure includes an active region ofa transistor. The active region includes a source/drain region, and thesource/drain region is defined at least in part by a first dopant havinga first dopant concentration. The source/drain region further includes asecond dopant with a concentration profile having a consistentconcentration from a surface of the source/drain region into a depth ofthe source/drain region. The consistent concentration is greater thanthe first dopant concentration. The structure further includes aconductive feature contacting the source/drain region at the surface ofthe source/drain region.

In an embodiment, the active region comprises a fin, and the transistoris a Fin Field Effect Transistor (FinFET). In an embodiment, thesource/drain region includes a germanium-containing material, and thesecond dopant includes a gallium-containing species. In an embodiment,the depth is at least 10 nm, and in another embodiment, the depth is atleast 5 nm. In an embodiment, the consistent concentration is greaterthan 1×10²¹ cm⁻³. In an embodiment, the structure further includes adielectric layer, and at least a portion of the conductive feature is inat least a portion of the dielectric layer. In an embodiment, theconductive feature includes a silicide at the surface of thesource/drain region and a contact to the silicide.

Another embodiment is a structure. The structure includes a substratecomprising a fin, and a gate structure over the fin. The fin has asource/drain region. The source/drain region includes agermanium-containing material, and the source/drain region furtherincludes a profile of a gallium concentration. The profile has aplatform at a surface of the source/drain region and decreases from theplatform into the source/drain region. The structure further includes asilicide region on the surface of the source/drain region, and a contacton the silicide region.

In an embodiment, the platform extends from the surface of thesource/drain region into the source/drain region at least 10 nm, and inanother embodiment, the platform extends from the surface of thesource/drain region into the source/drain region at least 5 nm. In anembodiment, the platform has a concentration greater than 1×10²¹ cm⁻³.In an embodiment, the source/drain region includes a dopant having aconcentration less than a concentration of the platform throughout thesource/drain region.

A further embodiment is a method. An active area on a substrate isdefined. The active area includes a source/drain region, and thesource/drain region is defined at least in part by a first dopant havinga first concentration. A second dopant is implanted into thesource/drain region. The second dopant has a consistent concentrationextending from a surface of the source/drain region to a depth in thesource/drain region. The consistent concentration is greater than thefirst concentration. A conductive feature is formed contacting thesource/drain region.

In an embodiment, the source/drain region includes agermanium-containing material, and the second dopant includes agallium-containing species. In an embodiment, implanting the seconddopant into the source/drain region amorphizes at least a portion of thesource/drain region. In an embodiment, the method further includesamorphizing at least a portion of the source/drain region includingimplanting an amorphizing impurity into the source/drain region beforeimplanting the second dopant. In an embodiment, the depth is at least 15nm, and in another embodiment, the depth is at least 10 nm. In anembodiment, defining the active area on the substrate includes definingthe source/drain region in the active area, and defining thesource/drain region includes epitaxially growing the source/drainregion. In an embodiment, epitaxially growing the source/drain regionincludes in situ doping the source/drain region with the first dopant.In an embodiment, a dielectric layer is formed over the source/drainregion, and an opening is formed through the dielectric layer to exposeat least a portion of the source/drain region. In an embodiment,implanting the second dopant is performed after forming the opening, andthe conductive feature is formed in the opening. In an embodiment, thedielectric layer is formed after implanting the second dopant, and theconductive feature is formed in the opening. In an embodiment, formingthe conductive feature includes forming a silicide at the surface of thesource/drain region, and forming a contact to the silicide.

Another embodiment is a structure. The structure includes a substrateincludes an active area. The source/drain region includes a dopanthaving a platform concentration of the dopant from a surface of theactive area to a first depth in the source/drain region and a decreasingconcentration of the dopant from the first depth to a second depth inthe source/drain region. The structure further includes a gate structureover the active area of the substrate and proximate to the source/drainregion, and a conductive feature over the substrate and contacting thesource/drain region.

In an embodiment, the active area includes a fin, and the gate structureis over the fin. In an embodiment, the source/drain region includessilicon germanium, and the dopant includes a gallium species. In anembodiment, the first depth is at least 10 nm, and in anotherembodiment, the first depth is at least 5 nm. In an embodiment, theplatform concentration is greater than 1×10²¹ cm⁻³. In an embodiment,the structure further includes a dielectric layer. In an embodiment, atleast a portion of the conductive feature is in at least a portion ofthe dielectric layer, and the conductive feature includes a silicide atthe surface of the active area and a contact to the silicide.

Another embodiment is a method. A gate structure is formed over anactive area of a substrate. A source/drain region is formed in theactive area and proximate the gate structure. After forming thesource/drain region, a dopant is implanted into the source/drain region.The dopant has a consistent platform concentration from a surface of thesource/drain region to a depth of the source/drain region. A conductivefeature is formed over the substrate and to the source/drain region.

In an embodiment, the source/drain region includes a silicon germaniummaterial, and the dopant includes gallium. In an embodiment, implantingthe dopant into the source/drain region amorphizes at least a portion ofthe source/drain region. In an embodiment, the method further includesamorphizing at least a portion of the source/drain region includingimplanting an amorphizing impurity into the source/drain region beforeimplanting the dopant. In an embodiment, the depth is at least 15 nm,and in another embodiment, the depth is at least 10 nm. In anembodiment, forming the source/drain region includes epitaxially growingthe source/drain region. In an embodiment, epitaxially growing thesource/drain region includes in situ doping the source/drain region withan additional dopant having a concentration less than the consistentplatform concentration. In an embodiment, forming the conductive featureincludes: forming a silicide at the surface of the source/drain region,and forming a contact to the silicide. In an embodiment, the methodfurther includes forming a dielectric layer over the source/drainregion, and forming an opening through the dielectric layer to expose atleast a portion of the source/drain region. In an embodiment, implantingthe dopant is performed after forming the opening, and the conductivefeature is formed in the opening. In an embodiment, the dielectric layeris formed over the source/drain region after implanting the dopant, andthe conductive feature is formed in the opening.

Another embodiment is a method. A fin is formed on a substrate. A gatestructure is formed over the fin. A source/drain region is defined inthe fin, and the source/drain region includes a germanium-containingmaterial. A gallium-containing dopant is implanted in the source/drainregion. The gallium-containing dopant has a concentration profile with aplatform from a surface of the source/drain region to a first depth inthe source/drain region and a decreasing gradient from the first depthto a second depth in the source/drain region. A conductive feature isformed to the source/drain region.

In an embodiment, implanting the gallium-containing dopant in thesource/drain region amorphizes at least a portion of the source/drainregion. In an embodiment, the method further includes amorphizing atleast a portion of the source/drain region including implanting agermanium-containing impurity into the source/drain region beforeimplanting the gallium-containing dopant. In an embodiment, the firstdepth is at least 15 nm, and in another embodiment, the first depth isat least 10 nm. In an embodiment, defining the source/drain regionincludes: forming a recess in the fin, and epitaxially growing thesource/drain region in the recess. In an embodiment, epitaxially growingthe source/drain region includes in situ doping the source/drain regionwith an additional dopant having a concentration less than the platformof the concentration profile. In an embodiment, forming the conductivefeature further includes: forming a silicide at the surface of thesource/drain region, and forming a contact to the silicide. In anembodiment, the method further includes: forming a dielectric layer overthe source/drain region, and forming an opening through the dielectriclayer to expose at least a portion of the source/drain region. In anembodiment, implanting the gallium-containing dopant is performed afterforming the opening, and the conductive feature is formed in theopening. In an embodiment, the dielectric layer is formed over thesource/drain region after implanting the gallium-containing dopant, andthe conductive feature is formed in the opening.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1.-12. (canceled)
 13. A method comprising: defining an active area on a substrate, the active area including a source/drain region, the source/drain region being defined at least in part by a first dopant having a first concentration; implanting a second dopant into the source/drain region, the second dopant having a consistent concentration extending from a surface of the source/drain region to a depth in the source/drain region, the consistent concentration being greater than the first concentration; and forming a conductive feature contacting the source/drain region.
 14. The method of claim 13, wherein the source/drain region comprises a germanium-containing material, and the second dopant comprises a gallium-containing species.
 15. The method of claim 13, wherein implanting the second dopant into the source/drain region amorphizes at least a portion of the source/drain region.
 16. The method of claim 13 further comprising amorphizing at least a portion of the source/drain region comprising implanting an amorphizing impurity into the source/drain region before implanting the second dopant.
 17. The method of claim 13, wherein the depth is at least 15 nm.
 18. The method of claim 13, wherein the depth is at least 10 nm.
 19. The method of claim 13, wherein defining the active area on the substrate comprises defining the source/drain region in the active area, wherein defining the source/drain region comprises epitaxially growing the source/drain region.
 20. The method of claim 19, wherein epitaxially growing the source/drain region comprises in situ doping the source/drain region with the first dopant.
 21. A method comprising: forming a first source/drain region in a semiconductor region; forming a platform dopant region in the first source/drain region, wherein a first concentration of a first dopant in the platform dopant region is constant from an upper surface of the semiconductor region to a first depth; forming a tailing dopant region in the first source/drain region, wherein a second concentration of the first dopant in the tailing dopant region decreases as the tailing dopant region extends away from the platform dopant region; and forming a contact to the platform dopant region.
 22. The method of claim 21, wherein the first dopant comprises gallium.
 23. The method of claim 21, further comprising amorphizing at least a portion of the first source/drain region prior to forming the platform dopant region.
 24. The method of claim 23, wherein the amorphizing is performed at least in part by implanting a second dopant, wherein the first dopant is different than the second dopant.
 25. The method of claim 21, wherein the first depth is about 8 nm.
 26. The method of claim 25, wherein the first depth is about 12 nm.
 27. A method comprising: forming a first source/drain region in a semiconductor region; implanting a first dopant into the first source/drain region to form an amorphous region; implanting a second dopant into the amorphous region, wherein the first dopant is different than the second dopant; and recrystallizing the amorphous region, wherein after recrystallizing, the first source/drain region comprises a platform dopant region and a tailing dopant region, the platform dopant region having a consistent doping profile of the second dopant to a first depth, the tailing dopant region having a decreasing concentration as the tailing dopant region extends into the semiconductor region from the platform dopant region.
 28. The method of claim 27, wherein the semiconductor region comprises silicon germanium and the first dopant comprises germanium.
 29. The method of claim 28, wherein the second dopant comprises gallium.
 30. The method of claim 27, wherein the consistent doping profile has a consistent concentration greater than 1×10²¹ cm⁻³.
 31. The method of claim 27, further comprising: forming a dielectric layer over the first source/drain region; forming an opening in the dielectric layer, wherein the opening exposes the platform dopant region; forming a first metal layer over the platform dopant region; annealing to cause the first metal layer to react with the platform dopant region to form a silicide region; and forming a second metal layer over the silicide region.
 32. The method of claim 27, wherein a depth of the tailing dopant region is at least 10 nm. 